Crystalline formation



March 21, 1944.

led June 11, 195'? 3 Sheets-Sheet l inal Fi Orig INVENTOR ATTQRNE YS iginal Filed June 11, 1937 3 Sheets-Sheet 2 INVENTOR ATTORNEYS March 21, 1944. A. M. MARKS CRYSTALLINE FORMATION 3 Sheets-Sheet 3 Original Filed June 11, 1937 Wm M v an /um ATTORNEY S Patented Mar. 21, 1944 A UNITED STATES PATENT OFFICE Alvin M. Marks, Beechhurst, Long Island, N.

Original application June 11, 1937, Serial No. 147,650. Divided and this application April 27. 1940', Serial No. 331,987

s Claims. ('01. 91-46) This invention relates to an apparatus for coating a support with an optically active crystalline coating and has particular application to coating a transparent supporting structure with a crystalline substance capable of polarizing incident light.

The object of the invention is to provide an improved apparatus for coating a crystalline substance on a supporting surface.

In the drawings,

Figures 1A and 1B are prints made from photomicrographs (enlarged respectively, 88 and 300 with a crystalline structure, the crystal of which has a natural tendency to grow more rapidly along its a: and y axes than along its z axis.

As described in; the above mentioned patent a supporting medium'having a clean surface oapable of taking a high polish (for example a glass plate) is coated with a substance having a flat crystalline structure (such as iodocinchonidine sulfate) by vertically supporting the plate and partially immersing it in an alcohol-water solution of iodocinchonidine sulfate. Then relative movement is caused to take place between the liquid level of the solution andthe surface of the plate while solvent is evaporated from the solution. This causes the crystalline substance to be rejected from the solution onto the plate surface in the proximity ,of the interfaces of the solution, atmosphere, and plate. The crystalline structure thus grown, while subject to lines of.

tomicrographs (enlarged, respectively, 88 and 300 times) of the crystalline structure as it may appear at a still later stage during the second step of the process;

Figures 4A through 40 show a series of prints made from photomicrographs of different crystalline fields that may be obtained with the first step of the process; figures A and A in this series are photomiorographs of the crystal field, enlarged, respectively, 88 and 300 times; prints B and B are photomicrographs, enlarged, respectively, 88 and 300 times; print C is a photomicrograph enlarged 88 times;

Figure 5 is a print of a photomicrograph of a crystal structure illustrating howa certain dominant crystalline alignment blocks out a recessive crystalline alignment;

Figure 6 is a perspective view of apparatus for coating plates; and

, Figure 'l is a vertical section taken on line of Figure 6.

. The present invention may be considered an improvement on that disclosed in my copending application Serial No. 662,090, now Patent No. 2,104,- 949, issued January 11, 1938, a method for depositing on a supporting surface a crystalline surface tension force (and to other lines of'force which may be present), when governing factors are properly. related, forms a coating of the iodocinchonidine sulfate on the plate that is substantially optically uniform and "complete," 1; e., substantially. without holes or interstices As described in the patent, such factors as the rate of relative movement of the solution surface and plate, the temperature of the solution, vibration, etc., are so regulated as to make the coating substantially complete.

In accordance with the present invention, I prefer so to relate governing factors during this deposition as to produce a crystal field crystalline structure, such as shown in Figures 1A and 13, to be deposited. The crystalline structure is preferably continuous in the sense that there is no complete break or disruption of the crystal field as it is being depositedQ But the crystal field is meshed in the sense that it is filled with microscopic interstices or open areas over which no crystal is deposited.

Referring to Figures 4, the crystal field may be of what 1 term an "island structure" I as shown in examples A, A, in which open areas, 2 for the most part join each other; or semi-.

the desired crystalline structure is easier-to control and desired uniformity is more easily obtained since factors tending to cause misalignment are rendered less effective. The coating' on such a plate is completed, 1. e., filled in," (or what I prefer to' call "intensifledb by momentarily covering the crystal field with a supersaturated solution of the same crystalline substance, or of a crystalline substance isomorphous with respect to the crystalline base. This treatment causes the crystalline structure. of the field V to grow along' its a: and y axes to fill in the open areas. Whilethe interstices are thus filling" the growth along the z axis is small in comparison with the growth along the a: and y axes, and the coating is of a substantially uniform thickness. Inasmuch as the optical orientation of the crystal field is substantially unifo'rmthroughout, the crystalline structure completed or grown from the intensification step is also substantially optically uniform.

Referring to Figures 6 and 7 the improved 'apparatus shown for depositing such a crystal field on the surface of a supporting medium comprises a glass tank 50 which contains the solution of the crystalline substance to be deposited.

the tank-and forms the supporting media on which the crystal field is deposited. The rest of the apparatus forms the means for relatively supporting and moving the tank and plates.

connecting plates ".11 which also form the ends of the pontoons.- To'keep the center of gravity of this float system'as low as desired by two vertical rods 8| secured to cross pieces 83 I which in turn are supported by the angle iron 51 extending around the top ofv the water tank. The lower ends of the rod M are connected by a metal spacing strip. 85. ably chromium plated and polished so as to provide a smooth contact for sleeves 81 attached to theipontoons and which slide over the rods. The

A stack of glass plates 5| suitably spaced from each other, as will be described, is suspended inv This part of the apparatus comprises an outer tank 53 formed from galvanized iron, or the like,

suitably supported by steel channel irons 55 sup-.

ported by massive standards, not shown, in such manner that the structure possesses suflicient mass to be substantially free from sway, vibration, sagging or the like. Around the top side of the tank 53 is an angle iron 51 .which rests on the channel irons and to which other parts of the apparatus may be suitably secured. The tank isfilled with water, or other suitable liquid to the desired level for starting a batch operation,v from a pipe line 59 having a valve 6i. layer of oil 63 havinga relatively low vapor pressure is kept on top of the. water to prevent evaporation of the water, such evaporation being undesirable or requiring additional heat as well and increasing the water vapor pressure above the tank.

Flow of liquid from the tank for the purpose the spacers and-the stack is clamped together by relative dimensions of the rods and sleeves are chosen to allow sufflcient clearance therebetween so that the sleeves will not grab the rods. With this constcuction the whole float assembly is free to follow minute changesin liquid level but at the I same time is constrained to move only vertically. The frame suspended between the pontoons for actually supportingth'e glass tank 58 is open at the top so that the glass tank is readily removable and replaceable-as desired. a Glass plates, after being suitably cleaned, are

stacked side by side andspaced at the top with,

Bakelite spacers ID (in the present embodiment of an inch thick) placed between juxtaposed corners ofadjacent plates. Cork washers ll of about the same size as the spacers are placed outside of theunp r corners of the end plates over clamping strips 9| and clamping bolts 93, the cork serted between the lower corners of the plates; The slight spreading of the plates and their reof lowering its liquid level at a controlled rate during the deposition is regulated by an orifice 85 in a pipeline 51. A trap is provided in the line 61 ahead of the orifice to catch dirt which might otherwise clog the orifice. A hand valve 661n the does not appreciably affect the head above the The tank is preferably constructed so that the liquid surface area is relatively large so that the orifice used may also be relatively large.

Tank 50, preferablyof glass or other material a not chemically active with the solution, is supported within the water tank 53 by means of a float comprising a frame structure 69 rigidly secured to oppositely disposed pontoons H and 13.

sil-iency holds the glass spacers in place.

An advantage vof this method of stacking the plates is that'the plates are accurately spaced and only glass comes into contact with the solution.

The stacked assembly of plates is supported withrespecttothe water tank 53 from a cross-piece 95. suitably supported above the -angle'iron 5'! by 7 strips 9|. The slots enable the stack to be adjusted with respect to the glass tankill.

- vibration on the stack plate. The vibration thus produced as shown, is in the plane of the plates 4 aboutthe axis-f0 ed by the cross piece 95..

With this assem iy, when the stack of plates is lowered into the solution in the tank 59 to maximum immersion, as at the start of the process, the solution in the tank 60 rises to a point near its top. The solution.between the plates creeps up abovethe main body of the solution in the tank 50. When conditions of equilibrium are suitably established, as will be described, the

valve in line 61 is openedand tank 50 starts lowering. The two pontoons are rigidly joined together by 76 Since rate of movement or the mam-as These rods are preferf plates with respect to the solution level in the I tank 50 is one of the factors governing the na lowering of the water level, the reducing of the immersion of the plates in the solution with the consequent rising of the pontoon in thewater HI. Burners Ill and H3 are relatively large and hand-controlled, and enable the temperature of the body of liquid in tank 53 to be brought rapidly to a temperature approximating that desired. Burner H5 is smaller and is regulated by means of a suitable off-on valve, controlled by a thermostat H1 during the preliminary heating, and by thermostat H9 during the deposition. The latter is supported from the float and so moves with it and is connected with binding posts by flexible leads. The heating system is so designed that a close temperature control of the water in tank 53 is obtained. This close control of the water maintains a close temperature control of the liquid in the tank 50.

After the desired temperature equilibrium has been established between the water, the solution and the stack of plates, the valve in pipe 61 is opened and the water level in tank 53 starts dropping. Simultaneously, however, the temperature of the solution causes evaporation of the solvent to take place substantially uniformly over the solution surface as well as over the solution between the plates and the crystalline solute is precipitated out on'the exposed surfaces of the I glass plates. The evaporation of the solution produces a lowering of the solution surface with respect to the plates and soproduces a relative velocity which hereinafter will be referred to as velocity due to evaporation, The water flowing out through the orifice also produces a relative movement between the solution level and the plates which will hereinafter be referred to as mass velocity.

Referring .to Figures 4 I have found that by varying various controlling factors different types of crystal fields may be deposited. The examples illustrated are obtained from depositing out iodocinchonidine sulfate. Among the controlling factors are per cent saturation of the body of the solution, temperature at which the deposition takes place, the distance d between opposing surfaces of the plates, relative movement between the solution surface and the plate surface due to mass velocity and others. These factors may be so related as to produce any one of the three types of crystal fields, or laceworks shown, or any intermediate step therebetween. Further, the contours of the crystals, or Joined crystal areas may vary from those shown which are illustrative only and are not intended as limiting.

Percent saturation to 40% saturation produced a structure having such open areas as shown in Example 4A; a 40% to saturation produced a structure such as shown in Example 43; a saturation produced a structure such as shown in Example 40; and a saturation produced a structure in which the coating is substantially complete. as

described in the above mentioned patent.

- Distance between plates Using a saturated solution of iodocinchonidine sulfate at 27 C. and keeping other factors constant and the mass velocity zero, but varying the distance between the plates and so varying the amount of solution between them, a distance d of V of an inch produced a structure such'as shown in Figure 4A; a distance d of 3 a of an inch produced a crystal field such as shown in Figure 4B; and a spacing of from to A; of an inch produced a structure such as shown in Figure ,4C; and a spacing of A of an inch or greater produced a substantially complete coating structure. With regard of this factor of spacing, it is evident from the above example that as the spacing between the plates is reduced the intemal movement of the solute in the solution between the plates is reduced so that the only deposit that can take place on the plates is of that solute which is in solution in the liquid between the plates at the start of the deposition.

Temperature and the mass velocity substantially zero, the effect of temperature on the crystalline structure is generally as follows: Using a saturated solution of iodocinchonidine sulfate at a temperature of 25 C., a structure such as shown in Figure 4B is obtained when using a spacing d of a; of an inch. A temperature of 35 C., however, gives a structure such as shownin Figure 40.

Further, as the temperature is increased, the rate of evaporation is increased and the rate of lowering due to evaporation is increased.

Velocity One of the effects of introducing a relative movement between the solution surface and plates by mechanical means i. e., the mass velocity, is to increase the area over which the solute being deposited is spread. Holding other factors constant, using a spacing d of a; of an inch, and

working at such temperatures as from 65 C. to 73 C., what might be termed relatively high mass velocities produce no deposit at all. But-as the velocity is reduced first a structure such as example A (Figure 4) is deposited out and as the velocity is reduced still further structures such as examples B, C, etc., are grown. In this connection there appears to be a maximum mass ve- Keeping the distance d less than it of anjinch and artists gms. per liter at 25': c. this solubility= 14.20 grams per liter which is the solubility at 61.8 c.

and assuming uniform evaporation over the entire surface of the solution. x

Let

solution) at temperature '1. 1n=grams of solute deposited per unit area on plate, gramspercm. Ve=downward velocity of the-liquid level relative'to theeplate produced by evaporation only Vm=downward "mass velocity, -cm./sec. Under this interpretation Va would be the downward velrocitz of-the liquid level relative to the plate,

if c= v,=(v.+'v,..) =Total downward velocity cm./sec.-

d=distanee between plates (less than ti"):

consider first the casewher'e V v-=0. Then MST Consider now the case where a velocity Va .is'

superimposed on the velocity V. so that the total velocity becomes (v.+v;.i=v,.

G=solubility of solute (grams of solute s; cc. of 5 mm; theefllne t, the-wclsht or solute in the solution evaporated is the same as in case 1: that is. (GdV. t) ems. per unit horizontally. However this weight of solute has now beeneoated over a total area equalling, MFA-Visit. The total weight equals m2(V+Va t) Hence (VA-via) I or v Gd m- 1)V. Equation 1 Now at temperature To holding v at were a c; a at temperatureT higher than To Keeping m=1n by increasing v... I Q! V, 61. d 2 V.'+ 2 m yin s a g: a Q

a GT0 where Q Q G00 Vis= (Q-l) Ve Equation II Vr=QV Equation III Giving numerical values to theexample: At temperature To (=25-C.)Q=1 since aces-s14 From Equation 11 it is evident that Va maybe made' very large by increasing the temperature:

v forced 'l G marrying v.

evaporation) 25' O. T 8.55 for 1-3 mmJday l-3 day 61.; 3 2 300mm./day lmmmfgrday Alignment of crystalline structure with. respect to the plane of the solution surface The crystalline structure of iodocinchonidine sulfate may deposit on the glass plate with itspolarizing axes at definite but different angles with respect to the plane of the solution surface.

For example, I have found that it may deposit out with the polarizing axes at approximately 0 to the solution surface; plus to the solution surface; plus 90 to the solution surface; plus 117 to the solution surface; and plus 135 to the solution surface.

By/plus and minus with respect to the solution surface I refer to the :i: coordinate, which. can be considered as extending vertically from the plane of the solution surface. The right hand quadrant formed by the a: axes I have referred to as plus and the left hand quadrant as being minus. Possibly there are other angles. To obtain a crystalline. coating on the supporting plate of substantially uniform optical orientation the process is so controlled and the constituents used are so selected as to cause one particular alignment with respect to the solution surface to dominate over all recessive alignments. Factors which have a direct bearing on the deposition alignment, as it may be called,-are the percent of water present in the solution'and the total velocity between the solution surface and the plate surfaces. These factors are'r'egulated to cause the crystal structure to form with the desired alignment.

With regard to the effect of the water content at a solution temperature of 66 0., if a relative velocity between the solution surface and the plates of about 4.5 inches per hour is used, a solution having 20 percent water tends to deposit a dominant crystalline structure whose polarizing axis is at approximately plus45 to the solution surface; using a solution having 28 percent tends to crystallize out a dominant crystalline structure whose polarizing axis is at 117 to the solution surface; using a solution having 40 percent water tends to crystallize out a dominant crystalline structure whose polarizing axis is at 90 to the solution surface.

The effect of increasing water percentage from 20% to 40% is demonstrated when crystals of Four times iodocinchonidine'sulfate are grown unsupported in a solution of the iodocin'chonidlne sulfate.

vits the water percentage is increased the length of the crystal grown increases so that the longest diagonal of the crystal gradually shifts with respect to the polarizing axis of the crystal. The shape of. an icdocinchonidinc' sulfate crystal grown from a solution having 29% water is such that its length approximately equals its breadth. Thus, if such a crystal is grown while subject to a velocity factor sumciently great to exert an aligning effect on the crystal, the crystalline structure deposited out has a 45 alignment, its longest diagonal being at 90 to the solution surface. But as the shape of the crystal is elongated by increasing the water percentage to,

28%, the alignment changes to plus 117, the longest diagonal still remaining at 90 to the solution surface. Thus the shape of the crystal deposited is a factor entering into the alignment, providing, however, that the velocity of movement between the solution surface on which the crystallization is taking place is suflicient to make the velocity a controlling factor.

The relationship between the above alignments and the relative water percentage holds true providing the velocity is suiiicient to exert a controlling effort. Thus, by increasing the velocity from one inch per hour to 4.5 inches per hour (using a water content of the dominant alignment shifts from 135 to 45, this latter alignment having a strong blocking out eflect on the recessive alignments. However, further increasing the velocity does not change the alignment but maintaining this same velocity, changing the percentage of water, does change the alignment as-pointed out.

With each of these percentages of water particles of dirt or other imperfections or upsetting factors may cause other alignments to startdepositing out along with the dominant alignment, the dominant alignment, however, eventually blocking out the recessive alignments.

Referring to Figure 5, the dark area marked R has an alignment of 90, whereas the dominant alignments are 45. As the process proceeded the 45 alignment kept blocking out the 90 alignment until eventually only the 45 alignment remained. The angle formed by the tapering out 90 alignment deposition becomes smaller and smaller as the velocity is increased above the optimum velocity. So it is desirable to regulate this velocity to the optimum value to keep the angle at which a non-desired alignment tapers out large enough to insure its being blocked out soon after it starts forming.

Another factor which apparently aids in enabling one alignment of the crystalline structure deposited to dominate overall other alignments which might deposit out is in causing the crystalline coating to deposit out in the form of desired crystal field. -Further, it enables "the a crystal fleld rather than in a form of a complete coating.

In the present embodiments the factors above discussed are preferably so governed and related as to cause the process to produce an open-mesh or semi-mesh crystal field uniformly oriented. To this end the plates are preferably placed so close together thatthe relationship of Equation I holds. Further, the temperature at which the process takes place (and consequently the solubility) is maintained as high as practicalso that the rate of mechanical movement may be made as high as practical. In addition to these factors the vibrator produces a vibratory motion between the solution surface and plates which aids in obtaining the desired uniform alignment.

In a preferred solution the iodocinchonidine sulfate apparently exists in at least three forms, all of which may be present in a 20% HzO-ethyl alcohol solution. The first form, which I call iodocinchonidine sulfate-a takes the form of flat almost symmetric crystals hexagonal or other shapes derived from an approximately 45 rhombic crystal and has the most desirable light polarizing properties since its extinction color is needles, or thread-like crystals. It is colorless on parallel transmission but red on extinction. When in a bulk form and wet wtih alcohol it is a maroon-brown fluffy mass, simflar to appearance to a colored wet absorbent cotton in water. The iodocinchonidine sulfate-a is stable at ordinary temperature in an ethyl-alcohol water solution up about 20-30% water. However, at high temperature it slowly decomposes to produce a quantity of iodocinchonidine sulfate-b. Additional heating causes the iodocinchonidine sulfate-b to change to iodocinchomdine sulfate-c.

Apparently while a small percent of iodocinchonidine sulfate-b is desirable because the elongated crystals of iodocinchonidine sulfate-b aid in blocking out the recessive alignment, presence of iodocinchonidine sulfate-c appears to interfere with the deposition of the desired crystal field by depressing the maximum velocity at which deposition will take place.

' To the end of obtaining a solution for depositing iodocinchonidine sulfate-a on a surface and obtaining the. desired proportions of iodocinchonidine sulfate-a and iodocinchonidine sulfate-b, the following method of preparing a solution has been found satisfactory:

Starting with a solution of 20% water, 4.77% methyl alcohol and 75.23% ethyl alcohol (this mixture is made up by using 16 parts distilled water to 84 parts denatured alcohol, formula 3A), 200 grams of iodocinchonidine sulfate manufactured as described in the above mentioned patent, is dissolved in 10 liters of the above solvent. This mixture is then heated at approximately 67 C. for from. three to four hours. This heating of the cinchonidine sulfate aids in the later deposition in' obtaining Z he process to deposit a uniform alignment more quickly at the start. The heat treated iodocinchonidine sulfate is then, by cooling, re-crystallized to about 28 C. to 30 C., and the crystals filtered and dried.

This heated cinchonidine sulfate hereinafter called iodocinchonidine sulfate-prime is again dissolved in the above solvent in the proportions of 20 grams of iodocinchonidine sulfate prime to each liter of solvents. To the mixture is also preferably added a long chain molecule, for example, 5 cc. of Pennsylvania motor oil, S. A. E. #30, per liter of solvent. This solution is placed in the glass tank 50 which is filled to its maximum height. The glass tank or jar is then placed in its rack in the float assembly. The rack may be conveniently removable from the float so as to, facilitate handling. Previously the water in the tank 53 has been heated by the large burners to approximately 71 C. and the control has been turned'over to the thermostat III which is set at 715 C. After the tank 50 has been immersed in the water, the liquid in it is relatively rapidly heated and when its temperature reaches about 68 0., the stack of glass plates (or; other supporting media having curved or flat surfaces sufliciently rigid to support the crystalline coating without so bending as to cause the coating to fracture) is lowered into tank 80, and the temperature is allowed to rise to about 64 0. Then thermostat Ill, set at a control point of 69 C. is turned on to take control of the heating of the water. This enables a temperature equilibrium between the solution in the tank 50, the stack of' glass'plates, and the water in the tank 53 to be established relatively rapidly. The temperature equilibrium thus established is such that the temperature in the tank50 is maintained at approximately 86' O.

The valve in the line 61 is now opened and the float is lowered. The nozzle 85 for this particular set-up and solution is preferably selected so as to produce a total relative motion between the bodyof liquid in the tank 50 and the plates of about 4.5 inches per hour. At this time also, of course, the vibrator is started.

After the liquid level in the tank 50 has travelled the full length of the stack of plates, the stack is removed, disassembled and intensified as hereinafter described.

Coming now to the second step, or intensification process: a super-saturated solution of iodocinchonidine sulfate-a in water and ethyl alcohol is made up so as to be super-saturated at several degrees above the temperature of the plate, to which it is to be applied. Assuming the temperature of the plates to be about 20 C.,

. such a solution may" be made by adding 8 mgs.

of iodocinchonidine sulfate-a to each cc. of a solvent comprising 16% water and 84% ethyl alcohol. This is heated to boiling and then quickly cooled to about 45 C. solution is applied to the crystalline mesh structure by placing the plate on a table with the crystalline structure upward and flowing the solution over it, allowing the solufion to: remain on the plate for about .20 seconds. During this time the plate is preferably vibrated in its plane to circulate the intensifying solution "and to aid in the crystal growth. The plate is then tippedand the solution poured off. The 1 plate is left for a few seconds more to allow time for further growth of the crystalline structure from the saturated solution. This procedure may be repeated two or three times in order to thicken the coating, for, naturally, after the first application during which all the inter-- stices are filled up. the crystalline structure'ij diunilcomprising a fir t nk holding a coatin grows along its 2 axis only, meaning the axis of its thickness.

Figures 1 through 3 show how the crystalline mesh fills up, or intensifies.

In carrying out the intensification process the temperature of the plate should be 5-to 25 below the temperature of the solution which is already at a temperature rendering it super-saturated. This is possible since iodocinchonidine sulfate-s has a wide range of supersaturation. As a result when the solution is flowed over the plate it is cooled further.- Thus, although its crystalline solute is depleted it tends'to remain super-saturated due to the further lowering of its temperature. This prevents any tendency for the crystalline structure on the plate to redissolve. a

' By increasing the water content of the supersaturated intensifying solution of iodoclnchonidine'sulfate and of other iodoalkaloid compounds, lithe crystal pressure tending to form crystal nuclei is reduced and less crystalline debris or unattached crystals'form' in the solution. Water contents (in a formula 3A solution) varying from 16% to 40% water are satisfactory. By directing a blast of air over the solution during the intensification step its super-saturated condition is maintained longer due to the cooling effect pro- 5 duced and to the evaporation of the solvent.

As the intensification solution becomes depleted, i. e., loses its super-saturation, it may :be run 011' and a fresh solution applied to increase further the amount of crystalline coating onthe tensifying solution is completed, the plate -is sprayed with a jet of clear rapid drying nitrocellulose lacquers in a suitable solvent such as ether and alcohol, present in sufilcient quantities to allow the lacquer to be sprayed as from a Jet. With a fine, or soft brush previously soaked in the lacquer and stroked over the plate, any superficial crystals of iodocinchonidine sulfate starting to grow on the surface of the crystalline structure are swept or sheared 0E and the film is rendered clear and optically uniform. The plate is then again washed with clear lacquer which is allowed to dry on the plate to form a protective coating.

- The application of the lacquer prevents further crystallization upon the crystalline film and so prevents the formation of any appreciable amount of debris on the crystalline structure.

This intensification process apparently works more satisfactorily when the interstices or holes are not more than I100 of an inch across the greatest dimensionfor, if the interstices have greater dimensions, a mechanically weaker coating may be formed.

That the intensification process produces a film of substantially uniform thickness is evident from a consideration of the fact that the rate of growth of the crystal is very slow along its z axis so that as the interstices are filling by crystal growth along the a: and u axes which is relatively rapid, any crystalline growth along the z 'axis is also effectively extended-to the new growth taking place as a result of the-intensification solution. s This application is a division of my copending application Serial No. 147,650, filed June 11, 1937, for Crystallinedormation, and which has matured to Patent Number 2,199,227, issued April 30,

Iclaim: l9 1. An apparatus for coating a supporting mesolution, a second tank having a liquid therein, a float means positioned to float in the liquid in said second tank, said. float means supporting said first tank, said first tank being thus movably supported within said second tank, means carried by said second tank for supporting a supporting medium above said first tank, said supporting medium- :being partially immersed in the solution 0 in said'first tank, means for withdrawing liquid from said second tank at a uniform rate to lower the liquid level therein.

2. An apparatus for coating a supporting medium comprising a first tank holding a coating 65 solution, a second tank having a liquid therein, a float means positioned to float in the liquid in said second tank. said float means supporting said first tank. said first tank being thus mova'bly supported within said Second tank, means carried by said second tank for supporting a supporting medium above said first tank, said supporting medium being partially-immersed in the solution in said first tank, means for withdrawing liquid from said second tank at a uniform rate to lower the liquid surface. After the final application of the in ior supporting a supporting medium above said first tank, said supporting medium being partially immersed in the solution in said first tank,

means for withdrawing liquid from' said second tank at a uniform rate to lower the liquid level therein, said means for withdrawing liquid from said second tank controlling the rate of movement produced by the float means to control the mass per unit area of the crystalline substance deposited on the supporting medium, and means for 10 controlling the temperature of the coating solution in said first tank.

7 ALVIN M. MARKS. 

